All telecommunications systems having multiple switching offices require signaling between the offices. The classic example relates to telephone networks. Telephone networks require signaling between switching offices for transmitting routing and destination information, for transmitting alerting messages such as to indicate the arrival of an incoming call, and for transmitting supervisory information, e.g. relating to line status. Signaling between offices can use `in-band` transport or `out-of-band` transport.
In-band signaling utilizes the same channel that carries the communications of the parties. In a voice telephone system, for example, one of the common forms of in-band signaling between offices utilizes multi-frequency signaling over voice trunk circuits. The same voice trunk circuits also carry the actual voice traffic between switching offices. In-band signaling, however, tends to be relatively slow and ties up full voice channels during the signaling operations. In telephone call processing, a substantial percentage of all calls go unanswered because the destination station is busy. For in-band signaling, the trunk circuit to the end office switching system serving the destination is set-up and maintained for the duration of signaling until that office informs the originating office of the busy line condition. As shown by this example, in-band signaling greatly increases congestion on the traffic channels, that is to say, the voice channels in the voice telephone network example. In-band signaling also is highly susceptible to fraud because hackers have developed devices which mimic in-band signaling.
Out-of-band signaling evolved to mitigate the problems of in-band signaling. Out-of-band signaling utilizes separate channels, and in many cases separate switching elements. As such, out-of-band signaling reduces congestion on the channels carrying the actual communication traffic. Also, messages from the end users always utilize an in-band format and remain in-band, making it virtually impossible for an end user to simulate signaling messages which ride on an out-of-band channel or network. Out-of-band signaling utilizes its own signal formats and protocols and is not constrained by protocols and formats utilized for the actual communication, therefore out-of-band signaling typically is considerably faster than in-band signaling.
Out-of-band signaling networks typically include data links and one or more packet switching systems. Out-of-band signaling for telephone networks is often referred to as Common Channel Signaling (CCS) or Common Channel Interoffice Signaling (CCIS). Most such signaling communications for telephone networks utilize signaling system 7 (SS7) protocol. An SS7 compliant CCIS network comprises data switching systems designated Signaling Transfer Points (STPs) and data links between the STPs and various telephone switching offices of the network.
In recent years, a number of new service features have been provided by an enhanced telephone network, sometimes referred to as an Advanced Intelligent Network (AIN). AIN type call processing relies heavily on signaling communication via the CCIS network. In an AIN type system, local and/or toll offices of the public telephone network detect one of a number of call processing events identified as AIN "triggers". For ordinary telephone service calls, there would be no event to trigger AIN processing; and the local and toll office switches would function normally and process such calls without referring to the central database for instructions. An office which detects a trigger will suspend call processing, compile a call data message and forward that message via a CCIS link to an Integrated Service Control Point (ISCP) which includes a Multi-Services Application Platform (MSAP) database. If needed, the ISCP can instruct the central office to obtain and forward additional information. Once sufficient information about the call has reached the ISCP, the ISCP accesses its stored data tables in the MSAP database to translate the received message data into a call control message and returns the call control message to the office of the network via CCIS link. The network offices then use the call control message to complete the particular call.
An AIN type network for providing an Area Wide Centrex service was disclosed and described in detail in commonly assigned U.S. Pat. No. 5,247,571 to Kay et al., the disclosure of which is entirely incorporated herein by reference. AIN type processing in such a system is controlled by the ISCP, which typically is operated by the local exchange carrier.
Similar intelligent services, particularly advanced 800 number services, may be offered by other carriers. Existing 800 number call processing utilizes a central 800 database (CMSDB) in a Service Control Point (SCP), to control switching operations through multiple end offices. Local and/or toll offices of the network detect dialing of an 800 number, suspend call processing, compile a call data message and forward that message via a CCIS link to the 800 database in the SCP. The SCP accesses stored data tables identified by the dialed 800 number to translate the received message data into a call control message, including a plain old telephone service (POTS) type destination telephone number. In this system, if the SCP does not currently store the destination number corresponding to a particular 800 number, the SCP will obtain the destination number from a national 800 database referred to as a Service Management System (SMS). The SCP transmits the call control message to the office of the network via CCIS link, and the network offices use the POTS destination telephone number in the call control message to complete the particular call.
Examples of 800 number call processing routines are disclosed in U.S. Pat. No. 4,191,860 to Weber, U.S. Pat. No. 4,611,094 to Asmuth et al. and U.S. Pat. No. 4,611,096 to Asmuth et al.
The intelligent call processing provided by the ISCP and SCP type centralized databases facilitates a wide range of services, many of which can be customized to meet the needs of individual subscribers. To service a large number of customers in this manner, particularly where every call to or from every intelligent service subscriber receives query and response processing through a centralized database, places a heavy signaling burden on the interoffice signaling network. Also, typically, a query and response cycle between a switching office and a remote database requires approximately 600 microseconds. Although this time appears short to a person placing a call, the delay is quite long in terms of electronic or computer processing capabilities by the switching offices. During this waiting time, resources of the switch that launched the call are sitting idle, reserved for the call but waiting for the response from the database. When multiplied by millions of calls, the waiting time burdens switching office resources that otherwise could be processing other calls and thereby generating additional revenue. As the number of intelligent services utilizing the query and response procedure continues to increase, the need for a more rapid technique to provide the necessary control information to the switching offices becomes increasingly acute.
Also, the various intelligent services provided through earlier systems have relied on `triggers` set in the individual switching offices. Occurrence of a call processing event recognized as a trigger causes the switching office to formulate a special application message in Transaction Capabilities Applications Protocol (TCAP). Triggers must be set in many individual offices, and each such office must formulate the specialized type messages. Upgrading individual switching offices to perform these functions is expensive.